Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like.
Over the years, the disk and the head have undergone great reductions in their size. Much of the refinement has been driven by consumer demand for smaller and more portable hard drives such as those used in personal digital assistants (PDAs), Moving Picture Experts Group audio layer 3 (MP3) players, and the like. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches. Advances in magnetic recording are also primary reasons for the reduction in size.
Modern drives often have very narrow tolerances for components and operation of components. Disk drive sliders are designed to fly in very close proximity to the disk surface. For instance, in some systems the slider may be designed to fly only three to five nanometers above the disk surface. In a system with such close tolerances, components can be subject to van der Waals, Meniscus, electrostatic, spindle motor charge up, and contact potential forces. These forces are due to a variety of causes, such as: the molecular attraction of components in very close proximity; adhesive friction caused by contact between the slider and the lubricant on the disk; the build up of electrical potential between the disk and the slider caused by the rotating disk surface (tribo-charging); the build up of electrical potential in motor bearings (tribo-charging); potential difference (e.g., contact potential difference/difference in work functions) that exists between two different metals (different Fermi levels of slider and disk material); and impacts between the slider and disk surface.
The drawings referred to in this brief description should be understood as not being drawn to scale unless specifically noted.